This disclosure is directed to a method for manufacturing polycarbonates.
Aromatic polycarbonates have been widely adopted for use as engineering plastics in many fields because of their excellent mechanical properties such as high impact resistance, heat resistance, transparency, and the like.
Polycarbonates can be manufactured by reacting an aromatic dihydroxy compound with a diaryl carbonate in the presence of a polymerization catalyst. For example, the method of making an aromatic polycarbonate generally comprises an ester interchange reaction (melt polymerization method) between an aromatic dihydroxy compound and a diaryl carbonate. It is noted that this method of manufacturing aromatic polycarbonates has attracted recent attention because it is inexpensive and does not employ phosgene and methylene chloride. As such, this method is more advantageous from an environmental perspective compared to other methods employing, for example, phosgene and methylene chloride.
Separation and reuse of volatile by-products and monomers from a polymerization reaction is important if a method to prepare polycarbonates is to be economically viable and environmentally safe. In particular, when the reaction produces phenol as a by-product, continuous recovery of phenol and volatile monomers and incorporation of the recovered monomers in polymerization contributes to long-term stable operation of the polymerization method.